1. Field of the Invention
The invention relates to the field of printing presses, and more specifically to an apparatus and method for cutting a web of print stock passing through a press into sheets of a predetermined length.
2. Description of the Related Art
In the printing industry, printed matter is often applied to a web of material which is fed off of a large roll into a printing press, such as a flexographic press. After the printing is done, the web must be cut into smaller sheets from which the final product will be formed.
Flexographic presses commonly use a rotating xe2x80x9cdie rollerxe2x80x9d or xe2x80x9csheeter rollerxe2x80x9d to perform the cutting step. The die roller is mounted in the press transversely to the web and includes a longitudinally mounted knife which rotates into contact with the web on each revolution of the die roller, cutting the web. Since a cut is made with every revolution of the die roller, the sheets produced by the press will have a length which is equal to the circumference of the die roller. In order to change the length of the sheets, the die roller is removed and a roller with a different circumference substituted in its place.
One problem with a sheeting apparatus as described is that it does not easily lend itself to cutting long sheets such as those required for banners, shelf liners, or edging material. In order to products of this type, the die roller would have to be of a prohibitively large circumference. Such a large roller would be difficult or impossible to mount in the press, would take up an unacceptable amount of space, and would be heavy and hard to handle. Another problem with this system is that changing out the die rollers each time the printer wishes to change sheet size is unnecessarily time consuming and labor intensive.
What is needed is a sheeting apparatus which is more flexible than the prior art system, which allows for the production of sheets of any length, and does not require parts to be interchanged in order to vary the sheet length.
The present invention comprises a sheeting apparatus for cutting a web of material passing through a printing press into sheets. The apparatus includes a rotating die roller including a knife mounted longitudinally thereon which is oriented transversely to and adjacent one side of the web. The die roller is slidably mounted to the printing press on tracks such that the die roller is moveable between an engaging position wherein the knife rotates into cutting engagement with the web and a released position wherein the knife does not contact the web. A pair of springs are provided which bias the roller into the released position. A pair of linear actuators are selectively operable to move the die roller into the engaging position in opposition to the spring bias. Operation of the actuators is controlled by a programmable controller which extends and retracts the actuators at intervals to produce sheets of a predetermined length. A counter operatively connected to the die roller counts full or partial revolutions of the die roller and transmits a signal to the controller representative of the count. The controller uses the signal to determine the intervals between cycles of the actuators.